The present invention relates to polymers containing compounds capable of removing oxygen from the materials with which the polymer comes in contact.
There are many products, particularly foods and beverages, which are sensitive to oxygen and suffer significant deterioration upon exposure to very low levels of oxygen. To extend the lifetime of oxygen sensitive products such as beer and fruit drinks there are many commercial containers that incorporate oxygen barriers and/or oxygen absorbers (scavengers). In these designs, an oxygen barrier is used to effectively reduce the permeation of oxygen into the package. For extremely sensitive products an oxygen absorber is used to chemically react with any oxygen permeating into the package or any oxygen trapped in the headspace during filling. Through careful design, the use of oxygen barrier and/or scavenger materials results in the creation and maintenance of extremely low oxygen levels within the container.
A polymeric material that is commonly used in packaging applications is polyethylene terephthalate or PET. This material has a number of valuable properties for packaging but lacks sufficient gas barrier for some applications. For example, although PET has adequate oxygen barrier properties for products which are relatively oxygen-insensitive such as carbonated soft drinks, its oxygen permeability limits its use in packaging for beer, fruit juices, other citrus products, tomato based products and aseptically packed meat. Multilayer structures have been proposed to improve PET""s gas barrier. Polymers that have excellent oxygen barrier (passive barrier) or scavenging properties (active barrier) are combined with PET to produce a layered structure consisting of the individual polymers. The methods disclosed for producing multilayer structures include co-injection, co-extrusion, lamination, and coating. Polymers which have been used to provide oxygen barrier include EVOH, PVOH, PVDC and polyamides such as m-xylylene diamine adipate. Blends of barrier polymers with PET have also been taught as a method to improve the oxygen barrier of packages. Some examples of polymers that have been blended with PET are PEN, EVOH, m-xylylene diamine adipate, liquid crystal polymers, and Mitsui""s B010.
Oxygen scavengers which have been disclosed to be useful include polymers capable of undergoing metal catalyzed oxidation such as m-xylylene diamine adipate or polybutadiene, oxidizable metals such as iron, or reduced anthraquinones. Oxygen absorbers that have been blended into PET include m-xylylene diamine adipate with a cobalt catalyst as well as modified polybutadienes incorporated through a reactive extruder.
Examples of scavengers incorporated into polyesters are known. For example, WO 98/12127 and WO 98/12244 disclose blends of PET containing either oxidizable metals or modified polybutadienes. However, these materials have no passive barrier and are hazy. Further, these blends introduce undesirable contaminants into existing PET recycle streams.
U.S. Pat. No. 5,2736,616 disclose oxygen scavengers containing certain pendant ether moieties. However the general class of polyether compounds of the present invention are not disclosed.
Neiman and Goglev (Vysokomol. Soyed. A9, No. 10, pp.2083-2093, 1967; as translated in Polymer Science U.S.S.R., vol. 9, pp.2351-2363, 1967, pub. 1968) disclose that oxygen is taken up during the thermal degradation of poly(propylene glycol) and poly(ethylene glycol) above their melting point. However, they do not disclose oxygen up-take in blends or copolymers of polyethers with other polymers. Furthermore, they do not disclose scavenging in the solid state or at room temperature. They are also silent on the use of transition metal catalyst or photoinitiators.
WO 99/48963 discloses oxygen scavenging compounds which include a polymer or oligomer having at least one cyclohexene group or functionality and a transition metal compound as a catalyst. Other oxygen scavenging compounds are not disclosed.
WO 99/15433 discloses oxygen scavenging polymeric substances which contain compounds which are devoid of ethylenic unsaturation and specifically a polyether oligomer (specifically polypropylene oxide) and a transition metal catalyst. Other polyethers are not disclosed to be effective scavengers when incorporated into a polymer with a catalyst.
Thus, there are several oxygen barrier and scavenging technologies known in the art, but none fully address the needs for an optimum package.
The present invention relates to oxygen scavenging systems comprising an oxidation catalyst and at least one polyether selected from the group consisting of poly(alkylene glycol)s, copolymers of poly(alkylene glycol)s and blends containing poly(alkylene glycol)s. The oxygen scavenging systems of the present invention are suitable for incorporating into articles containing oxygen-sensitive products. The present invention further relates to novel compositions comprising: a poly(alkylene glycol), an oxidation catalyst and a thermoplastic polymer.
The present invention relates to oxygen scavenging systems comprising an oxidation catalyst and at least one polyether selected from the group consisting of unsubstituted poly(alkylene glycol)s having alkylene chains of 1 to 3 carbon atoms, substituted or unsubstituted poly(alkylene glycol)s having alkylene chains of at least 4 carbon atoms, copolymers of poly(alkylene glycol)s and blends containing poly(alkylene glycol)s. The oxygen scavenging systems of the present invention can be incorporated into a variety of polymers. The oxygen scavenging systems of the present invention act as an active oxygen barrier by scavenging oxygen from whatever is in contact with the article containing the oxygen scavenging system.
Polymers comprising the oxygen scavenging systems of the present invention can be used as layers in rigid containers, flexible film and in thermoformed, foamed, shaped or extruded articles and the like for packaging oxygen-sensitive products or use in oxygen sensitive environments. The articles containing the composition limit oxygen exposure by acting as an active oxygen barrier and/or a means for scavenging oxygen from within the article.
Suitable articles include, but are not limited to, film, sheet, tubing, profiles, pipes, fiber, container preforms, blow molded articles such as rigid containers, thermoformed articles, flexible bags and the like and combinations thereof Typical rigid or semi-rigid articles can be formed from plastic, paper or cardboard cartons or bottles such as juice containers, soft drink containers, beer containers, soup containers, milk containers, thermoformed trays or cups. In addition, the walls of such articles often comprise multiple layers of materials. This invention can be used in one, some, or all of those layers.
The first component of the oxygen scavenging systems of the present invention is at least one polyether. Suitable polyethers include unsubstituted poly(alkylene glycol)s having alkylene chains of 1 to 3 carbon atoms, substituted or unsubstituted poly(alkylene glycol)s having alkylene chains of at least 4 carbon atoms and preferably less than 10 carbon atoms. The poly(alkylene glycol)s can be obtained by methods well known in the art. Examples of poly(alkylene glycol)s include poly(ethylene glycol), poly(trimethylene glycol), poly(tetramethylene glycol), poly(pentamethylene glycol), poly(hexamethylene glycol), poly(heptamethylene glycol), and poly(octamethylene glycol). Preferred poly(alkylene glycols) include poly(ethylene glycol) and poly(tetramethylene glycol). Almost any number of repeating units may be used, however, for ease of handling and mixing poly(alkylene glycols) having number average molecular weights in the range of about 500 to about 5,000 are preferred. Suitable poly(alkylene glycol)s may have a variety of suitable end groups, including, but not limited to hydroxyl, epoxy, methyl and the like. Preferred end groups include methyl and hydroxyl.
The amount of the poly(alkylene glycol) may vary, so long as the desired scavenging effect is provided and final composition can be formed into the desired article. Preferred amounts for scavenging include at least about 1 weight % poly(alkylene glycol), preferably at least about 4 weight % and more preferably at least about 8 weight % and most preferably between about 10 and about 15 weight % poly(alkylene glycol). Poly(alkylene glycol) copolymers of various glycol units may also be used in the present invention. The copolymers may be alternating, random, segmented, block, graft, or branched. Examples of poly(alkylene glycol) copolymers include poly(ethylene glycol)-ran-poly(propylene glycol), poly(ethylene glycol)-block-poly(propylene glycol)-block-poly(ethylene glycol) and poly(propylene glycol)-block-poly(ethylene glycol)-block-poly(propylene glycol). Preferred amounts include at least about 2 weight % and preferably at least about 4 weight %.
In addition to poly(alkylene glycol)s, polyethers comprising polymeric or oligomeric ethers derived from cyclic ether monomers can be used as the oxidizable component of the polymer. For example, poly(2,3-dihydrofurandiyl), prepared by cationic polymerization of 2,3-dihydrofuran, can be incorporated into an oxygen scavenging composition in the same fashion as the above-mentioned poly(alkylene glycol)s. Additional examples include polymers derived from monomers of structure I or II, where n +m can be an integer between 3 and 10, and R1, R2, R3, R4, R5, and R6 are independently, a hydrogen atom or a lower alkyl group of 1 to 4 carbons or halogen: 
The lower alkyls represented by R1, R2, R3, R4, R5, and R6 in the monomer units I and II may be the same or different and include, alkyls having up to four carbon atoms, such as methyl, ethyl, propyl, isopropyl, butyl, or the like.
It is also possible for the polymeric and oligomeric ethers to be functionalized at their respective terminal ends with reactive functionality for copolymerization, grafting, or reactive extrusion into or on other polymer compositions. These polyethers may have number average molecular weights in the range of about 5,000 to about 200,000 (as determined by gel permeation chromatography using a polystyrene standard) and be used in amounts between about 1 weight % and about 25 weight %.
Cyclical ethers, such as those commonly referred to as crown ethers, can be used as the oxidizable component of the polymer. For example, 18-crown-6 (hexaoxacyclooctadecane, III) can be incorporated into an oxygen scavenging composition in the same fashion as the above-mentioned poly(alkylene glycol)s. Some types of crown ethers are suitably functionalized with reactive groups for copolymerization, grafting, or reactive extrusion into or on other polymer compositions. Those trained in the art should recognize that there are many cyclic ethers available for use without detracting from the intent. 
Suitable oxidation catalysts include transition metal catalysts which can readily interconvert between at least two oxidation states. Preferably, the transition metal is in the form of a transition metal salt with the metal selected from the first, second or third transition series of the Periodic Table. Suitable metals include manganese II or III, iron II or III, cobalt II or III, nickel II or III, copper I or II, rhodium II, III or IV and ruthenium I, II or IV. Suitable counterions for the metal include, but are not limited to, chloride, acetate, acetylacetonate, stearate, palmitate, 2-ethylhexanoate, neodecanoate or naphthenate. The metal salt may also be an ionomer, in which case a polymeric counterion is employed. Such ionomers are well known in the art. Any amount of catalyst which is effective in catalyzing oxygen scavenging may be used. Preferred amounts include at least about 10 ppm, preferably between about 200 and about 500 ppm.
The thermoplastic polymer may be present at concentrations of 0 to 99.99 weight % of the total composition. Thermoplastic polymers which are suitable in the present invention include polyesters, polyolefins, polyamides, polyurethanes, styrene containing polymers and copolymers, polyacrylates, epoxy-amines, polyvinyl chloride, acrylonitrile containing polymers and copolymers, vinylidene chloride containing polymers and copolymers, polycarbonates, and ethylene copolymers such as ethylene-vinyl acetate, ethylene-vinyl alcohol, ethylene-alkyl (meth)acrylates, ethylene-(meth)acrylic acid and ethylene-(meth)acrylic ionomers. Blends of different thermoplastic polymers may also be used. Preferred thermoplastic polymers for food packaging applications include polyesters, polyamides, polyolefins, polycarbonates and EVOH.
Suitable polyesters include at least one diacid and at least one glycol. The primary dibasic acids are terephthalic, isophthalic, naphthalenedicarboxylic, 1,4-cyclohexanedicarboxylic acid, phenylenedioxydiacetic acid and the like. The various isomers of naphthalenedicarboxylic acid or mixtures of isomers may be used but the 1,4-, 1,5-, 2,6-, and 2,7-isomers are preferred. The 1,4-cyclohexanedicarboxylic acid may be in the form of cis, trans, or cis/trans mixtures. The various isomers of phenylenedioxydiacetic acid or mixtures of isomers may be used but the 1,2-, 1,3-, and 1,4- isomers are preferred. In addition to the acid forms, the lower alkyl esters or acid chlorides may also be used.
The dicarboxylic acid component of the polyester may optionally be modified with up to about 95 mole percent of one or more additional dicarboxylic acids. Such additional dicarboxylic acids include dicarboxylic acids having from 6 to about 40 carbon atoms, and more preferably dicarboxylic acids selected from aromatic dicarboxylic acids preferably having 8 to 14 carbon atoms, aliphatic dicarboxylic acids preferably having 4 to 12 carbon atoms, or cycloaliphatic dicarboxylic acids preferably having 7 to 12 carbon atoms. Examples of suitable dicarboxylic acids include phthalic acid, isophthalic acid, naphthalene-2,6-dicarboxylic acid, cyclohexanedicarboxylic acid, cyclohexanediacetic acid, diphenyl-4,4xe2x80x2-dicarboxylic acid, 1,3-phenylenedioxydiacetic acid, 1,2-phenylenedioxydiacetic acid, 1,4-phenylenedioxydiacetic acid, succinic acid, glutaric acid, adipic acid, azelaic acid, sebacic acid, and the like. Polyesters may be prepared from one or more of the above dicarboxylic acids. Preferably said dicarboxylic acid comprises up to about 25 mole %, and more preferably 15 mole % at least one additional dicarboxylic acid.
Typical glycols used in the polyester include aliphatic glycols containing from two to about ten carbon atoms, and cycloaliphatic glycols containing 7 to 14 carbon atoms. Preferred glycols include ethylene glycol, 1,4-butanediol, 1,6-hexanediol, 1,4-cyclohexanedimethanol, diethylene glycol and the like. The glycol component may optionally be modified with up to about 50 mole percent, preferably up to about 25 mole % and most preferably up to about 15 mole % of one or more different diols. Such additional diols include cycloaliphatic diols preferably having 6 to 20 carbon atoms, aromatic diols containing from 6 to 15 carbon atoms or aliphatic diols preferably having 3 to 20 carbon atoms. Examples of such diols include: diethylene glycol, triethylene glycol, 1,4-cyclohexanedimethanol (when using 1,4-cyclohexanedimethanol, it may be the cis, trans or cis/trans mixtures), propane-1,3-diol, butane-1,4-diol, pentane-1,5-diol, hexane-1,6-diol, 3-methylpentanediol-(2,4), 2-methylpentanediol-(1,4), 2,2,4-trimethylpentane-diol-(1,3), 2-ethylhexanediol-(1,3), 2,2-diethylpropane-diol-(1,3), hexanediol-(1,3), 1,4-di-(2-hydroxyethoxy)-benzene, 2,2-bis-(4-hydroxycyclohexyl)-propane, 2,4-dihydroxy-1,1,3,3-tetramethyl-cyclobutane, 2,2-bis-(3-hydroxyethoxyphenyl)-propane, 1,3-bis(2-hydroxyethoxy)benzene, 1,4-bis(2-hydroxyethoxy)benzene, 2,2-bis-(4-hydroxypropoxyphenyl)-propane, 4,4xe2x80x2-sulfonyldiphenol, resorcinol, hydroquinone and the like. Polyesters may be prepared from one or more of the above diols.
The polyester resin may also contain small amounts of trifunctional or tetrafunctional comonomers such as trimellitic anhydride, trimethylolpropane, pyromellitic dianhydride, pentaerythritol, and other polyester forming polyacids or polyols generally known in the art.
The polyesters of the present invention can be made by conventional processes well known in the art, and need not be described here.
Suitable polyolefins of the present invention include mono- and diolefins, for example polypropylene, polyisobutylene, polybut-1-ene, poly-4-methylpent-1-ene, polyisoprene, or polybutadiene, and also polymers of cycloolefins, for example cyclopentene or norbornene; furthermore polyethylene (which can be crosslinked), for example high-density polyethylene (HDPE), high-density polyethylene of high molar mass (HDPE-HMW), high-density polyethylene of ultra high molar mass (HDPE-UHMW), medium-density polyethylene (MDPE), low-density polyethylene (LDPE), linear low-density polyethylene (LLDPE) and branched low-density polyethylene (VLDPE).
Mixtures of the polymers described above, for example mixtures of polypropylene with polyisobutylene, polypropylene and polyethylene (e.g. PP/HDPE, PP/LDPE) and mixtures of different types of polyethylene (e.g. LDPE/BHDPE).
Suitable copolymers of monoolefins and diolefins with each other or with other vinyl monomers are disclosed in WO 97/30112 and W097/11993.
Suitable polyamides include partially aromatic polyamides, aliphatic polyamides, wholly aromatic polyamides and mixtures thereof By xe2x80x9cpartially aromatic polyamidexe2x80x9d it is meant that the amide linkage of the partially aromatic polyamide contains at least one aromatic ring and a nonaromatic species.
Wholly aromatic polyamides comprise in the molecule chain at least 70 mole % of structural units derived from m-xylylene diamine or a xylylene diamine mixture comprising m-xylylene diamine and up to 30% of p-xylylene diamine and an xcex1xcex5-aliphatic dicarboxylic acid having 6 to 10 carbon atoms, which are further described in Japanese Patent Publications No., 1156/75, No. 5751/75, No. 5735/75 and No. 10196/75 and Japanese Patent Application Laid-Open Specification No. 20 29697/75.
Polyamides formed from isophthalic acid, terephthalic acid, cyclohexanedicarboxylic acid, meta- or para-xylylene diamine, 1,3- or 1,4-cyclohexane(bis)methylamine, aliphatic diacids with 6 to 12 carbon atoms, aliphatic amino acids or lactams with 6 to 12 carbon atoms, aliphatic diamines with 4 to 12 carbon atoms, and other generally known polyamide forming diacids and diamines can be used. The low molecular weight polyamides may also contain small amounts of trifunctional or tetrafunctional comonomers such as trimellitic anhydride, pyromellitic dianhydride, or other polyamide forming polyacids and polyamines known in the art.
Preferred partially aromatic polyamides include: poly(m-xylylene adipamide), poly(hexamethylene isophthalamide), poly(hexamethylene adipamide-co-isophthalamide), poly(hexamethyl adipamide-co-terephthalamide) and poly(hexamethylene isophthalamide-co-terephthalamide). The most preferred partially aromatic polyamide is poly(m-xylylene adipamide).
Preferred aliphatic polyamides include polycaprolactam (nylon 6), poly- aminoheptanoic acid (nylon 7), poly-aminonanoic acid (nylon 9), polyundecane-amide (nylon 11), polylaurolactam (nylon 12), polyethylene-adipamide (nylon 2,6), polytetramethylene-adipamide (nylon 4,6), polyhexamethylene-adipamide (nylon 6,6) polyhexamethylene-sebacamide (nylon 6,10), polyhexamethylene-dodecamide (nylon 6,12), polyoctamethylene-adipamide (nylon 8,6), polydecamethylene-adipamide (nylon 10,6), polydodecamethylene-adipamide (nylon 12,6) and polydodecamethylene-sebacamide (nylon 12,8). The most preferred aliphatic polyamide is poly(hexamethylene adipamide). Partially aromatic polyamides, are preferred over the aliphatic polyamides where good thermal properties are crucial.
The polyamides of the present invention can be made by conventional processes well known in the art, and need not be described here.
Various additives, which are known in the art may also be included in the thermoplastic polymers of the present invention. Such additives include, but are not limited to colorants, pigments, toners, carbon black, glass fibers, fillers, impact modifiers, antioxidants, stabilizers, flame retardants, reheat aids, acetaldehyde reducing compounds, adhesion promoters, recycling release aids, passive barrier aids and the like.
The poly(alkylene glycol) may either be physically blended with the thermoplastic polymer, covalently bound to the thermoplastic polymer in the form a copolymer or combinations thereof.
The physical blends may be prepared by combining the poly(alkylene glycol) and thermoplastic polymer using melt blending equipment such as Brabender extruder equipment, single-screw extruders, twin-screw extruders and the like. Properties of the blends may be altered significantly depending on the mixing temperature and mixing time. The poly(alkylene glycol) and thermoplastic polymer may be combined just prior to film or sheet extrusion or injection molding into an article.
Thermoplastic polymers copolymerized with poly(alkylene glycol)s may also be blended with the thermoplastic polymers. For example, thermoplastic elastomers containing polytetramethylene glycol such as DuPont""s HYTREL, Atofina""s PEBAX or Eastman Chemical Company""s ECDEL may be blended with a thermoplastic polymer such as PET.
Those skilled in the art will recognize that many polymer/poly(alkylene glycol) combinations are possible without detracting from the spirit of this invention.
Poly(alkylene glycol)s may be covalently bound to the thermoplastic polymer to form a copolymer. The poly(alkylene glycol)/thermoplastic polymer copolymer may be a segmented copolymer, a block copolymer or a graft copolymer. Examples of poly(alkylene glycol)/thermoplastic polymer copolymers that may be used in the oxygen scavenging composition include but are not limited to polyester/poly(alkylene glycol), polyamide/poly(alkylene glycol), polyurethane/poly(alkylene glycol), polyolefin/polyalkylene glycol, acrylic/poly(alkylene glycol) and polycarbonate/poly(alkylene glycol) copolymers. Ethylene-vinyl alcohol/poly(alkylene glycol) graft copolymers may also be used in the present invention.
A polyester/poly(alkylene glycol) copolymer can be formed from at least one diacid, at least one glycol and at least one poly(alkylene glycol). The composition of the poly(alkylene glycol) is described above and will have either hydroxyl, epoxy, carboxylic acid or amine end groups and either be monofunctional or difunctional. The polyester/poly(alkylene glycol) copolymer may contain up to 99 weight percent of the poly(alkylene glycol). The composition of the polyester in the polyester/poly(alkylene glycol) copolymer is the same as the thermoplastic polyesters described above.
Polyester/poly(alkylene glycol) copolymers can be produced by conventional, well-known processes. One such process is the esterification of one or more dicarboxylic acids with one or more glycols. In another process, one or more dialkyl esters of dicarboxylic acids undergo transesterification with one or more glycols in the presence of a catalyst such as a salt of manganese, zinc, cobalt, titanium, calcium, magnesium or lithium. In either case, the monomer and oligomer mixture is typically produced continuously in a series of one or more reactors operating at elevated temperature and pressures at one atmosphere or greater. Alternately, the monomer and oligomer mixture could be produced in one or more batch reactors. Suitable conditions for esterification and transesterification include temperatures between 200 to about 250xc2x0 C. and pressures of about 0 to about 80 psig. It should be understood that generally the lower the reaction temperature, the longer the reaction has to be conducted.
Next, the mixture of polyester monomer and oligomers undergoes melt-phase polycondensation to produce a low molecular weight precursor polymer. The precursor is produced in a series of one or more reactors operating at elevated temperatures. To facilitate removal of excess glycols, water, alcohols, aldehydes, and other reaction products, the polycondensation reactors are run under a vacuum or purged with an inert gas. Inert gas is any gas not causing an unwanted reaction. Suitable gases include, but are not limited to partially or fully dehumidified air, CO2, argon, helium and nitrogen. Catalysts for the polycondensation reaction include salts of antimony, germanium, tin, lead, or gallium, preferably antimony or germanium. Reaction conditions for polycondensation include a temperature less than about 290xc2x0 C., and preferably between about 240xc2x0 C. and about 290xc2x0 C. at a pressure sufficient to aid in removing undesirable reaction products such as ethylene glycol. Precursor inherent viscosity (IhV) is generally below about 1.5 dL/g. The target IhV is generally selected to balance good color and minimize the amount of solid stating required. IhV was measured at 25xc2x0 C. using 0.50 grams of polymer per 100 ml of a solvent consisting of 60% by weight phenol and 40% by weight tetrachloroethane. The low molecular weight precursor polymer is typically produced continuously in a series of one or more reactors operating at elevated temperature and pressures less than one atmosphere. Alternately low molecular weight precursor polymer could be produced in one or more batch reactors.
After pelletization of the low molecular weight precursor polymer, the pellets may be fed directly into an extruder, or solid stated at conventional conditions until the desired molecular weight is attained.
Another key feature of the invention is that the precursor is crystallized and undergoes further polycondensation in the solid state by conventional, well-known processes, such as those disclosed in U.S. Pat. No. 4,064,112. Solid state polycondensation can be conducted in the presence of an inert gas as defined above, or under vacuum conditions, and in a batch or continuous process. The polyester can be in the form of pellets, granules, chips or powder.
The poly(alkylene glycol) may be added directly into the melt phase reactor during esterification, prepolymer or polycondensation stages. If this method is used it is desirable to add the poly(alkylene glycol) at a point in the reactors where there is good mixing to insure homogeneous distribution of the poly(alkylene glycol) throughout the polymer melt. The poly(alkylene glycol) may be added undiluted directly to the polymer melt or incorporated into a liquid carrier and added to the polymer melt. If a liquid carrier is used the poly(alkylene glycol) may be incorporated into the liquid carrier at concentrations of 1 to 99 weight percent. The liquid carrier may be any organic solvent or water. Preferably, the liquid carrier is ethylene glycol.
In an alternate embodiment the poly(alkylene glycol) may be added to the molten polyester composition after completion of polycondensation but prior to strand extrusion and pelletizing. This addition may be accomplished in a variety of ways. For example, the poly(alkylene glycol) may be added undiluted or incorporated into a low molecular weight, polymeric or liquid carrier prior to addition to the molten polyester.
In another embodiment the poly(alkylene glycol) may reacted with the thermoplastic polymer, (c), in a reactive extrusion or reactive compounding step that is performed subsequent to manufacture of the thermoplastic polymer, (c). Conditions of the operation can be adjusted to provide varying degrees of reaction between the poly(alkylene glycol) and the thermoplastic polymer, (c).
The method of this invention can initiate oxygen scavenging in a composition, layer, or packaging article solely prepared from the oxidizable organic compound and transition metal catalyst without photoinitiator. However, components such as photoinitiators or antioxidants can be added to further facilitate or control the initiation of the oxygen scavenging properties.
For instance, it is often preferable to add a photoinitiator, or a blend of different photoinitiators, the compositions used to prepare the oxygen scavenger, if any antioxidants are included to prevent premature oxidation of that composition.
Suitable photoinitiators are well known to those skilled in the art. Preferably, photoinitiators have little absorbance in the visible range (greater than about 400 nm), good absorbance outside the absorbance range for the thermoplastic polymer and have low volatility at temperatures used for their incorporation. Specific examples include, but are not limited to 2,3-butanedione, substituted aryl ketones, such as benzophenone, o-methoxybenzophenone, acetophenone, o-methoxy-acetophenone, acenaphthenquinone, methyl ethyl ketone, valerophenone, hexanophenone, xcex1-phenylbutyrophenone, p-morpholinopropiophenone, dibenzosuberone, 4-morpholinobenzophenone, benzoin, benzoin methyl ether, 4-o-morpholinodeoxybenzoin, p-diacetylbenzene, 4-aminobenzophenone, 4xe2x80x2-methoxyacetophenone, xcex1-tetralone, 9-acetylphenanthrene, 2-acetylphenanthrene, 10-thioxanthenone, 3-acetylphenanthrene, 3-acetylindole, 9-fluorenone, 1-indanone, 1,3,5-triacetylbenzene, thioxanthen-9-one,xanthene-9-one, 2(4) isopropyl thioxanthen-9-one, 7H-benz[de]anthracen-7-one, benzoin tetrahydropyranyl ether, 4,4xe2x80x2-bis(dimethylamino)-benzophenone, 1xe2x80x2-acetonaphthone, 2xe2x80x2-acetonaphthone, acetonaphthone, benz[a]anthracene-7,12-dione, 2,2-dimethoxy-2-phenylacetophenone, xcex1,xcex1-diethoxyacetophenone, xcex1,xcex1-dibutoxyacetophenone, and the like. Singlet oxygen generating photosensitizers such as Rose Bengal, methylene blue, tetraphenyl porphyrin, and zinc phthalocyanine may also be employed as photoinitiators as well. Polymeric photoinitiators include poly(ethylene carbon monoxide), and oligo[2-hydroxy-2-methyl-1-[4-(1-methylvinyl)phenyl]propanone]. Use of a photoinitiator is preferable because it generally provides faster and more efficient initiation. When actinic radiation is used, the initiators may also provide initiation at longer wavelengths that are less costly to generate and are less harmful. Preferred initiators include 10-thioxanthenone, thioxanthen-9-one, xanthene-9-one and 2(4) isopropyl thioxanthen-9-one. Suitable amounts include any amount capable of initiating scavenging and preferable from about 10 ppm to about 10,000 ppm (1 wt %).
Antioxidants may also be added. Suitable antioxidants include hindered phenols, phosphites, primary or secondary antioxidants, hindered amine light stabilizers and the like. Antioxidants such as 2,6-di-(t-butyl)-4-methylphenol (BHT), 2,2xe2x80x2-methylene-bis(6-t-butyl-p-cresol), triphenylphosphite, tris-(nonylphenyl)phosphite, Irganox 1010 and dilaurylthiodipropionate would be suitable, but not limited to, for use with this invention. Suitable amounts include any amount capable of suppressing oxidative degradation and preferable from about 10 ppm to about 10,000 ppm (1 wt %).
As mentioned above, antioxidants may be used with this invention to control scavenging initiation. An antioxidant as defined herein is any material that inhibits oxidative degradation or cross-linking of polymers. Typically, such antioxidants are added to facilitate the processing of the polymeric materials and/or prolong their useful lifetime. In relation to this invention, such additives prolong the induction period for oxygen scavenging given an insufficient thermal history or in the absence of irradiation (photoinitiation). Then when the layer""s or article""s scavenging properties are required, the layer or article (and any incorporated photoinitiator) can be exposed to radiation, or alternatively, exposed to a sufficient temperature profile.
This material can be used as a layer in a multilayer structure, prepared by co-injection, co-extrusion, lamination, and coating. These multilayer structures can be formed into articles by any forming technique known in the art such as blow molding, thermoforming, and injection molding. When the poly(alkylene glycol) is incorporated into polyester, its interfacial properties will be better matched with adjacent layers of PET or other polyesters which will minimize delamination problems, thereby removing the possibility of structural failure or reduced clarity. Also, since the entire structure will be a polyester, existing recycling mechanisms will still be available for use.
Incorporating a poly(alkylene glycol) with a gas barrier polymer such EVOH will result in a material that has both gas barrier and oxygen scavenging properties. These compositions would be particularly useful in applications such as beer packaging requiring barrier to carbon dioxide egress and very low oxygen ingress.
Alternatively, the oxygen scavenging compositions of the present invention may be incorporated into one layer, and a gas barrier polymer may be incorporated into another. Suitable multilayer structures include three layer structures where the oxygen scavenging compound is incorporated into center layer, four layer structures where the oxygen scavenging compound is incorporated into at least one of the intermediate layers and five layer structures where the oxygen scavenging compound may be incorporated into either the center layer or the second and fourth layers. In four and five layer articles the additional internal layers may comprise performance polymers such as barrier polymers, recycled polymer and the like. Additionally the oxygen scavenging compounds of the present invention may be blended with recycled polymers. Generally the inner and outermost layers will be made from virgin polymer which is suitable for the desired end use. Thus, for example, for a food or beverage container, the inner and outermost layers would be made from a suitable polyester, such as PET.